The research objectives comprise a broad but integrated program which places special emphasis upon the elucidation of the cell-mediated and antibody mediated components of transplantation immunity and their interactions in three particular circumstances: a) in the maternal- fetal relationship; b) in the development of refractoriness to graft- versus-host disease; and c) in prolongation of allograft survival in privileged sites, such as the anterior chamber of the eye, in which the grafts acquire a rich blood supply but no lymphatic drainage. By the procedures of adoptive and passive immunization and blastocyst transfer, attempts will be made to find out more precisely how maternal-fetal histoincompatibility operates as an important determinant of implantation and the growth rate of the feto-placental unit. Appropriate labeling studies will be undertaken to determine both the magnitude and the locus of the natural maternal yields fetal passage of cells which takes place firstly, across the placenta and secondly during suckling in very young rats. Nearly all these objectives bear upon the question as to how specific genes produce their effects, and upon the interaction between cells leading to cellular and humoral responses and the regulation of the latter.